Preparation of 1-olefins

ABSTRACT

A multi-stage synthesis is effective for preparing 1-olefins from aldehydes. The aldehyde is condensed with acetone to form an α,β-unsaturated ketone. The unsaturated ketone is hydrogenated to yield a saturated alcohol. By dehydrating the saturated alcohol a 1-olefin is obtained. The olefin can be isolated in high yield and purified.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to the preparation of 1 -olefins fromaldehydes by means of a three-stage synthesis.

[0003] 2. Discussion of the Background

[0004] Owing to their reactivity, olefins are among the most importantsynthetic building blocks in organic chemistry. They are precursors formany compounds, for example aldehydes, ketones, alcohols, carboxylicacids and halogen compounds. They are used in large quantities for thepreparation of homo-oligomers or co-oligomers and homopolymers andcopolymers, for example polyethylene or polypropylene.

[0005] Ethylene and propylene are prepared in large quantitiesthroughout the world by steam cracking or by catalytic cracking ofhydrocarbons. These processes also produce considerable amounts ofC₄-olefins (isobutene, 1-butene, 2-butenes) and to a lesser extentC₅₁-olefins. Higher 1-olefins are mostly produced by chain buildupreactions.

[0006] Ethylene can be oligomerized with the aid of Ziegler catalysts togive a mixture of unbranched 1-olefins having an even number of carbonatoms.

[0007] In a variant of the SHOP process, unbranched 1-olefins having aneven or odd number of carbon atoms can be prepared from ethylene. Thisprocess comprises three reaction steps, namely ethylene oligomerization,isomerization, i.e., a shift of the double bonds, and cross-metathesisof the olefin mixture having internal double bonds with ethylene.

[0008] Dehydrogenation of straight-chain paraffins, for example bychlorination and dehydrochlorination, forms olefins having predominantlyinternal double bonds which can be converted by cross-metathesis into1-olefins. The above-mentioned processes all have the disadvantage thata large number of 1-olefins is always produced.

[0009] Straight chain 1-olefins having an even number of carbon atomscan be obtained from fatty alcohols by elimination of water.Disadvantages of this method are the high price of the startingmaterials and the fact that essentially only fatty alcohols having from12 to 18 carbon atoms are available in sufficient quantities.

[0010] Since the known methods do not give all desired 1-olefins in asufficiently large quantity and/or in a sufficiently high purity, thereis a need for a method of preparing 1-olefins from readily availablestarting materials.

[0011] It has now been found that 1-olefins can be prepared fromaldehydes by aldol condensation with acetone, hydrogenation of theα,β-unsaturated ketones to form the unsaturated alcohols and subsequentelimination of water from alcohols.

SUMMARY OF THE INVENTION

[0012] The invention accordingly provides a process for preparing1-olefins having from 7 to 24 carbon atoms from aldehydes having from 4to 21 carbon atoms, which comprises condensing an aldehyde with acetoneto form an α,β-unsaturated ketone, hydrogenating the unsaturated ketoneobtained in this way to form the saturated alcohol and eliminating waterfrom the saturated alcohol.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawing,wherein: a schematic diagram of the reaction apparatus is presented.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views.

[0015] In the process of this invention, it is possible to use aldehydesor aldehyde mixtures having from 4 to 21 carbon atoms. The aldehydesused can originate from various sources. It is possible to use aldehydeswhich have been obtained by dehydrogenation of alcohols, for example,fatty alcohols. Likewise, aldehydes from cleavage reactions, for exampleheptanal from methyl ricinoleate, can be used as starting materials. Inparticular, it is possible to use aldehydes which have been produced byhydroformylation of olefins.

[0016] Furthermore, unsaturated aldehydes formed by self-condensation ofan aldehyde, e.g., 2-ethylhex-2-enal from n-butyraldehyde, can also beused.

[0017] For example, the aldehydes mentioned below can serve as startingmaterial for the process of the invention:

[0018] n-butyraldehyde, isobutyraldehyde, crotonaldehyde, valeraldehyde,2-methylbutanal, 3-methylbutanal, dimethylpropanol, tiglinaldehyde,3,3-dimethylacrolein, n-hexanal, isohexanal, n-heptanal, citral, α- andβ-citral, benzaldehyde, cinnamaldehyde, phenylacetaldehyde,hydrocinnamaldehyde, 2-phenylpropionaldehyde, cyclohexyl carbaldehyde,anisaldehyde; aldehyde mixtures prepared by hydroformylation ofdipropene, dibutene, tripropene, tetrapropene, tributene, pentapropene,tetrabutene.

[0019] A preferred starting material is n-pentanal.

[0020] The aldol condensation of aldehydes with acetone to formα,β-unsaturated ketones is preferably carried out as a two-phasereaction. The reaction is, as described in DE 199 57 522, the disclosureof which is hereby expressly incorporated by reference, carried out in atube reactor, with the catalyst being present in the continuous phaseand the starting material being present in a disperse phase and theloading factor B of the reactor being equal to or greater than 0.8 andthe mass ratio of the catalyst phase to organic phase being greater than2. (The loading factor B is defined as follows: B=PD/PS. PD [Pa/m] is apressure dropper unit length over the reactor under operating conditionsand PS [Pa/m] is a mathematical parameter having the dimensions ofpressure per unit length, defined as the ratio of mass flow M [kg/s] ofall components under operating conditions multiplied by g=9/81 [m/s²],i.e., PS=(M/V)*g.)

[0021] As catalyst phases, preference is given to using aqueoussolutions of hydroxides, hydrogen carbonates, carbonates andcarboxylates in the form of their alkali metal or alkaline earth metalcompounds, in particular sodium hydroxide and potassium hydroxide. Theconcentration of the catalyst in the catalyst solution is from 0.1 to15% by mass, in particular from 0.1 to 5% by mass.

[0022] Aldehyde, acetone and optionally a solvent are introduced intothe catalyst phase upstream of the reactor. The molar ratio of aldehydeto acetone is from 5/1 to 1/10, preferably from 1/1 to 1/5. The reactionis carried out in a temperature range from 40° C. to 150° C., preferablyin the range from 50° C. to 120° C. The reaction time is from 0.1 to 20minutes, preferably from 0.2 to 10 minutes.

[0023] The catalyst phase is separated off from the product mixtureleaving the reactor and is recirculated to the reactor. Before the phaseseparation, unreacted starting materials, some product, water andoptionally solvent are preferably distilled off. After condensation, thedistillate separates into an aqueous phase and an organic phase which isreturned to the reactor. Starting materials, in particular acetone, aredistilled off from the aqueous phase and part of the aqueous phase isthen discarded to discharge the water of reaction from the system andpart of it is, after optional use as scrubbing liquid, returned to theprocess. The product phase which has been separated off from thecatalyst can, if desired after scrubbing with water, be worked up bydistillation to give the pure α,β-unsaturated ketone. Anotherpossibility is to use the crude product in the next stage. Thisprocedure enables the desired α,β-unsaturated ketone to be preparedhighly selectively.

[0024] Any organic solvent added to the starting material or to theproduct mixture from the reaction has to have the following properties:it dissolves products and starting materials and is itself sparinglysoluble in the catalyst phase. It is inert toward the aldol condensationand optionally in the hydrogenation. It can be separated by distillationfrom the intermediate, namely the α,β-unsaturated ketone and/or thesubsequent product, namely the saturated alcohol. Preferred solvents arethose which form a minimum heteroazeotrope with water, so that water caneasily be separated from the α,β-unsaturated ketone by distillation.Examples of suitable solvents are ethers, hydrocarbons such ascyclohexane or toluene.

[0025] The unsaturated ketone obtained as intermediate can not only beconverted into a 1-olefin as claimed in the process of the presentinvention but can also be utilized for other syntheses. Thus,hydrogenation of the unsaturated ketone can give a saturated ketone.This product could be an intermediate for a saturated alcohol or anolefin having an internal double bond.

[0026] The α,β-unsaturated ketone obtained by crossed aldol condensationaccording to the process of the invention is hydrogenated in pure formor as a mixture which can further comprise acetone, starting aldehyde,water, solvent and high boilers to give the corresponding saturatedalcohols.

[0027] The hydrogenation is preferably carried out in the liquid phase.

[0028] The hydrogenation can be carried out using catalysts or catalystsystems which hydrogenate both olefinic double bonds and carbonylgroups. Particularly useful catalysts for the hydrogenation of theα,β-unsaturated ketones are, in particular, those which are used for thehydrogenation of 2-ethylhex-2-enal to 2-ethylhexanol.

[0029] The hydrogenation can be carried out using, for example,copper/nickel, copper/chromium, copper/chromium/nickel, zinc/chromium,nickel/molybdenum catalyst. It is also possible to use combinations oftwo or more catalysts. The catalysts can be unsupported or thehydrogenation-active substances or their precursors can have beenapplied to supports such as silicon dioxide or aluminum oxide.

[0030] Preferred catalysts over which the α,β-unsaturated ketones arehydrogenated comprise 0.3-15% by mass of copper, 0.3-15% by mass ofnickel and, as activators, 0.05-3.5% by mass of chromium andadvantageously 0.01-1.6% by mass, preferably 0.02-1.2% by mass, of analkali metal component on a support material, preferably aluminum oxideor silicon dioxide. The amounts stated are based on the catalyst beforeit is reduced. The alkali metal component is optional.

[0031] The catalysts are advantageously used in a form in which theyoffer a low resistance to flow, e.g., in the form of granules, pellets,or shaped bodies such as tablets, cylinders, rod extrudates or rings.They are advantageously activated, e.g., by heating in a stream ofhydrogen, before use.

[0032] The hydrogenation, preferably a liquid-phase hydrogenation, isgenerally carried out under a total pressure of from 5 to 200 bar, inparticular from 5 to 30 bar, very particularly preferably from 15 to 25bar. A hydrogenation in the gas phase can also be carried out at lowerpressures with correspondingly large gas volumes. If a plurality ofhydrogenation reactors are employed, the total pressures in theindividual reactors can be identical or different within theabove-mentioned pressure limits.

[0033] The reaction temperatures in the hydrogenation in the liquid orgaseous phases are generally in the range from 120 to 220° C., inparticular from 140 to 180° C.

[0034] Examples of such hydrogenations are described in patentapplications EP 0 470 344 A2 and EP 0 326 674 A2.

[0035] The hydrogenation of 3-octen-2-one to octan-2-ol can optionallybe carried out in two stages. In this case, the olefinic double bond ishydrogenated over, for example, a palladium catalyst in the first stageand the carbonyl group is hydrogenated over one of the above-mentionedcatalysts in the second stage.

[0036] The saturated alcohols obtained in the second reaction step areused in the third step of the process of the invention. Furthermore,they can also be used as solvents or for producing plasticizers ordetergents.

[0037] The elimination of water from 2-alcohols generally gives amixture of 1- and 2-olefins. The catalytic dehydration of 2-alcohols toform predominantly 1-olefins is known from the literature. Thus, forexample, gas-phase processes in which the elimination of water iscarried out in the temperature range from 250 to 350° C. over aluminumoxide or zirconium oxides are disclosed in U.S. Pat. Nos. 5,130,287,5,210,363, GB 1225559 and GB 1233020.

[0038] Accordingly, the preparation of the 1-olefins is carried out inthe process of the invention by dehydration of 2-alcohols in the gasphase or a gas/liquid mixed phase over a fixed-bed catalyst.

[0039] The reaction mixture can, if desired after removal of water, beseparated by distillation into starting alcohol, olefins andby-products. The unreacted alcohol can be returned to the dehydrationstep.

[0040] If the olefin fraction further comprises olefins other than thetarget product, the pure 1-olefin can be isolated from it bydistillation.

[0041] The 1-olefins obtained by the process of the invention can beused as monomers or comonomers in the preparation of oligomers orpolymers. They can serve as starting compounds for the preparation ofepoxides, ketones, aldehydes, alcohols and carboxylic acids.Furthermore, they can be used as alkylating agents or as components indiene reactions. Monobranched olefins, in particular those having amethyl branch on the second or penultimate carbon atom, are suitable forpreparing tertiary carboxylic acids by the Koch synthesis. Here, theimportant fact is not the position of the double bond but the type ofbranching which is determined, inter alia, by the process of theinvention.

[0042] The advantage of the process of the invention is that 1-olefinscan be prepared from readily available aldehydes, with the degree ofbranching of the olefin prepared corresponding to that of the startingaldehyde. Thus, for example, 1-octene can be prepared from n-pentanalwhich can be obtained by hydroformylation of linear butenes.

[0043] The following examples illustrate the invention withoutrestricting its scope.

EXAMPLE 1 Condensation of Acetone and Pentanal to form 3-octen-2-one

[0044] The first table accompanying example 1 shows firstly the catalystcomposition and then the amount of feed and its composition. The productcomposition is listed in the lower part of the second table. The upperpart of the second table reports the space-time yield (STY), theconversion (C) of the aldehyde, the selectivity (S) to the desired aldolcondensation products and the loading factor (B). In the case of thecatalyst composition described, it should be noted that the values givenin the examples are initial values. The proportion of NaOH was slightlydiluted by water of reaction formed in the aldol condensation.Furthermore, the Cannizzaro reaction which proceeds in parallel to thealdol condensation leads to neutralization of the alkaline catalyst.However, both effects are so small over the time in question that theyare inconsequential for the description of the experiment and theexperimental result.

[0045] The aldolization was carried out in a test apparatus which isshown schematically in the drawing. Here, the continuous catalyst phase2 is circulated by means of a pump 1. The aldehyde or the aldehydemixture is mixed into the catalyst via line 3 or different aldehydes aremixed in separately via lines 3 and 4. In the example described below,the starting materials were mixed in exclusively via line 3. Themultiphase mixture 5 is pumped through the tube reactor 6 which has alength of 3 m and a diameter of 17.3 mm and was provided with staticmixing elements having a hydraulic diameter of 2 mm. The resultingmixture 7, comprising the reaction product, unreacted starting materialand the catalyst, can be freed of volatile constituents in the gasseparator 8 by discharge of the latter into line 9. In the exampledescribed below, this line was closed.

[0046] The liquid stream 10 obtained after the degassing step 8 ispassed to a phase separation vessel 11. Hence, the aqueous catalystphase 2 is separated off and returned to the circuit. The organic phasewhich has flowed over a weir and contains the reaction product is takenoff via line 12.

[0047] The heat of reaction can be removed by heat exchangers 13, 14 and15 located outside the reactor.

[0048] The example describes aldol condensation of acetone (Ac) andpentanal (PAL) to form 3-octene-2-one (3-ON). The formation of theby-products 4-methyl-3-penten-2-one (4-MP),4-hydroxy-4-methyl-3-pentan-2-one (4-HMP), 4-hydroxy-3-octan-2-one(4-HON), 2-propyl-2-heptenal (2-PHL) and the other high boilers (HB) arereported in % by mass in the table below.

[0049] The reaction mixture was passed through the reactor at a catalystthroughput of 400 kg/h at a temperature 80° C. under the autogenouspressure of the reaction participants. TABLE 1 Catalyst [g] 4981 c NaOH[% by mass] 4.0 Water [% by mass] 91.8 Acetone [% by mass] 4.2 Feed[1/h] 4.28 Ac [% by mass] 48.04 PAL [% by mass] 51.96

[0050] The following result was achieved: TABLE 2 STY [t/m³/h] 2.1 C [%]0.95 S [%] 64.0% B 14.72 Ac [% by mass] 22.52 PAL [% by mass] 3.04 4-MP[% by mass] 0.35 4-HMP [% by mass] 0.23 3-ON [% by mass] 47.46 4-HON [%by mass] 8.03 2-PHL [% by mass] 9.49 HB [% by mass] 8.88

[0051] In Table 2, the selectivity relates to the formation of3-octen-2-one; based on the sum of 3-octen-2-one and4-hydroxy-3-octan-2-one, the selectivity is 74%.

EXAMPLE 2 Hydrogenation of 3-octen-2-one to Form 2-octanol

[0052] One liter of a mixture obtained from the crude reaction productof example 1 by distilling off the low boilers, acetone and pentanal washydrogenated in the liquid phase in a circulation apparatus for 3 hoursat 160° C. and 25 bar absolute over 100 g of a Cu/Cr/Ni catalyst on anAl₂O₃ support. The analysis of the feed and the composition of thehydrogenation product after running the experiment for 3 hours are shownin Table 3. TABLE 3 Feed for the Product of the Hydrogenationhydrogenation Component (% by mass) (% by mass) Acetone 0.01 0.01Pentanal 0.25 0.00 Isopropanol 0.00 0.95 1-Pentanol 0.00 1.733-Octen-2-one 63.65 0.00 2-Octanol 0.00 73.25 4-hydroxy-3-octan-2-one10.79 0.00 3-Octan-2-one 0.00 1.05 4-Methyl-3-penten-2-one 0.48 0.004-Hydroxy-4-methyl-3-penten-2-one 0.35 0.05 4-Methyl-2-pentanol 0.000.72 2-Propyl-2-heptanal 12.72 0.00 2-Propylheptanol 0.00 12.15 Highboilers 11.75 10.09

[0053] As can be seen from Table 3, 3-octen-2-one and4-hydroxy-3-octen-2-one are hydrogenated with high selectivity (>97%) tothe desired product 2-octanol.

EXAMPLE 3 Dehydration of 2-octanol to Give 1-octene

[0054] The output from the hydrogenation in Example 2 was freed of lowboilers (pentanol isopropanol) and high boilers by distillation in alaboratory distillation apparatus and then used as starting materialcomprising about 98% by weight of 2-octanol and about 2% by weight ofhigh boilers for the dehydration in the presence of an NaOH-modifiedzirconium oxide (ZrO₂ containing 1% by weight of Na₂O) in a flow-throughfixed-bed reactor. Before entering the reactor, the liquid feed wasvaporized at 220° C. in an upstream vaporizer. At a reaction temperatureof 325° C. in the rector, 20.1 g/h (=24.5 ml/h) of feed were passed asgas through 35.7 g (−30 ml) of catalyst in pellet form, corresponding toan LHSV of 0.82 h⁻¹. The gaseous product was cooled in a condenser andcollected in liquid form in a glass receiver.

[0055] The GC analysis of the dehydration product is shown in Table 4.TABLE 4 Dehydration of 2-octanol over a ZrO₂ catalyst Products of thecracking of 2-octanol Component (% by weight) 1-Octene 57.60 tr-4-Octene0.00 tr-3-Octene/cis-4-octene 0.01 cis-3-Octene 0.02 tr-2-Octene 1.73cis-2-Octene 0.99 2-Octanone 7.10 2-Octanol 29.55 Dioctylether 0.25 Highboilers 0.25

[0056] As can be seen from Table 4, the 2-octanol is dehydrated withhigh selectivity (>95%) to the desired product 1-octene. After thedesired product and the by-products have been separated off bydistillation, the unreacted 2-octanol can be returned to the dehydrationreactor. The 2-octanone formed as by-product can be hydrogenated to2-octanol.

[0057] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

[0058] German applications DE 101 06 185.4 and DE 101 47775.9, filed onFeb. 10, 2001 and Sep. 27, 2001 respectively, are incorporated herein byreference.

1. A process for preparing one or more 1-olefins which comprisescondensing an aldehyde with acetone to form an α,β-unsaturated ketone,hydrogenating said α,β-unsaturated ketone to form a saturated alcohol,and eliminating water from said saturated alcohol to form said one ormore 1 olefins, wherein said aldehyde has from 7 to 24 carbon atoms andsaid one or more olefins has from 4 to 21 carbon atoms.
 2. The processas claimed in claim 1, wherein the condensation is carried out in a tubereactor having a loading factor of greater than 0.8.
 3. The process asclaimed in claim 1, wherein the hydrogenation is carried out in theliquid phase.
 4. The process as claimed in claim 1, wherein theα,β-unsaturated ketone is hydrogenated over a fixed-bed catalyst, saidfixed-bed catalyst comprising copper, chromium, and nickel, to form thesaturated alcohol.
 5. The process as claimed in claim 1, wherein theelimination of water from the saturated alcohol is carried out in thegas phase or in a gas/liquid mixed phase over a fixed-bed catalyst. 6.The process as claimed in claim 1, wherein the 1-olefin is 1-octene andthe aldehyde is n-pentanal.
 7. The process as claimed in claim 1,wherein the condensation takes place in the presence of a catalyst. 8.The process as claimed in claim 7, wherein said catalyst is sodiumhydroxide or potassium hydroxide.
 9. The process as claimed in claim 1,wherein a molar ratio of the aldehyde to the acetone is from 1/1 to 1/5.10. The process as claimed in claim 1, wherein the temperature is from50° C. to 120° C.
 11. The process as claimed in claim 1, wherein anorganic solvent is present.
 12. The process as claimed in claim 11,wherein the organic solvent is an ether or a hydrocarbon.
 13. Theprocess as claimed in claim 12, wherein the hydrocarbon is cyclohexaneor toluene.
 14. The process as claimed in claim 4, wherein the fixed bedcatalyst comprises from 0.3 to 15% copper, from 0.3 to 15% nickel andfrom 0.05 to 3.5% chromium by mass.
 15. The process as claimed in claim1, wherein the pressure is from 15 to 25 bar.
 16. A process forpreparing a polymer comprising polymerizing a 1-olefin obtained by theprocess as claimed in claim
 1. 17. A process for preparing a tertiarycarboxylic acid comprising oxidizing a 1-olefin obtained by the processas claimed in claim 1.